1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method for the same. In particular, the present invention relates to a semiconductor device that is used as a rectifying device and employs a pn junction. The present invention also relates to a manufacturing method for the same.
2. Description of the Related Art
In general, semiconductor devices used in high frequency switching, employ high speed recovery diodes. These diodes have a pn junction between a P type semiconductor region and an N type semiconductor region. The lifetime of the carrier is shortened by the diffusion of a heavy metal, such as platinum, known as a xe2x80x98lifetime killer.xe2x80x99
Referring now to FIG. 21, a longitudinal cross-section of a high speed recovery diode includes an N type semiconductor substrate 11. An N type semiconductor layer 12 has a lower carrier density than semiconductor substrate 11.
Semiconductor layer 12 is formed on top of semiconductor substrate 11 by epitaxial growth. An Active region 13 and a guard ring region 14 are formed by patterning an oxide film 15, layered on top of semiconductor layer 12, and using oxide film 15 as a mask, P-type impurities are ion injected. After the ion injection, the surface of semiconductor layer 12 is again covered by oxide film 15 through heat treatment. A section of oxide film 15 is removed in order to expose active region 13. After heat diffusion of platinum, a front electrode 16 is formed on top of active region 13. A back electrode 17 is formed on the back surface of semiconductor substrate 11.
The above-described diode is sometimes used in power factor improvement circuits (PFC). In general, diodes used for this purpose must have soft recovery characteristics in which the reverse recovery current is small and the current attenuation factor after the peak of the reverse current during reverse recovery is small.
When the reverse recovery current is large, this leads to an undesirable increase in the turn on loss for a MOS transistor frequently used as a switching element on the power factor improvement circuit (PFC) and also leads to an undesirable rise in temperature of the element.
If the attrition rate is large, a large voltage noise is generated and added onto the power voltage, and by having this voltage applied to the diode and MOS transistor, the element can be destroyed and errors in the circuit may result.
With the related art pn junction diode shown, there is an attempt to reduce the reverse recovery current by shortening the carrier lifetime by controlling the platinum diffusion conditions. However, there is a xe2x80x98tradeoffxe2x80x99 between the forward voltage of the diode and the reverse recovery current, and the forward voltage of the diode increases. Furthermore, controlling the platinum diffusion conditions alone does not solely reduce the attrition rate of the reverse current during reverse recovery. As a result, an adequate soft recovery is not achieved.
In addition to platinum concentration, the thickness of semiconductor layer 12 and the anode carrier concentration are optimizable, but when the thickness of semiconductor layer 12 increases, there is a corresponding increase in the forward voltage, and the tradeoff is worsened.
With pn junction diodes, in which platinum is diffused, as the xe2x80x98lifetime killerxe2x80x99 platinum piles up near the surface of the diode in a region and at a depth of several micrometers. Therefore, the beneficial effect of the platinum is not adequate near pn junctions that are deeper than several micrometers. As a result, the improvement in the xe2x80x98tradeoffxe2x80x99 is inadequate, and there is little if any improvement in the soft recovery characteristics.
To provide an adequate effect of platinum near the pn junction, the injection amount of platinum may be increased. Unfortunately, if the injection amount is increased, not only does the N-type semiconductor layer become high resistance, but defects are increased due to the high platinum concentration in the P-type active region, resulting in at least an increase in leakage current.
It is an object of the present invention to provide a semiconductor device and manufacturing method for the same which overcomes the drawbacks of the related art noted above.
It is another object of the present invention to provide a semiconductor device and a manufacturing method for the same which provides a diode with high speed as well as soft recovery characteristics.
The present invention relates to a semiconductor device and a manufacturing method for the same wherein a N-type semiconductor layer with a low impurity concentration is grown by epitaxial growth on top of a N-type semiconductor substrate. An oxide film with a desired pattern is formed on the surface of the semiconductor layer. Using the oxide film as a mask, an active region edge and a guard ring region are formed by ion injection. After formation, the portion that forms the active region is exposed, and a paste containing platinum is coated onto the back surface of semiconductor substrate, and heat diffusion of platinum occurs. Through this process, a region near the surface of the active region of semiconductor layer reverses to a P-type, and a reverse region is shallowly formed producing a fast diode with adequate soft recovery characteristics.
According to an embodiment of the present invention, there is provided a semiconductor device, comprising: a semiconductor region being a first conductive type, a reverse region being a second conductive type, the reverse region selected in a first surface of the semiconductor region, the reverse region being formed by platinum doping at a higher concentration near the first surface of the semiconductor region than in an interior portion of the semiconductor region, and the semiconductor region and the reverse region forming a pn junction.
According to another embodiment of the present invention, there is provided a semiconductor device, wherein: at least a first portion of the first surface of the semiconductor region being covered by at least an oxide film, and the reverse region being formed in a first region corresponding to an open window of the oxide film.
According to another embodiment of the present invention, there is provided a semiconductor device, further comprising: at least a first electrode electrically contacting the reverse region, at least a second electrode electrically contacting the semiconductor region, at least one impurity diffusion region being the second conductive type surrounding the reverse region in at least a first zone, and the impurity diffusion region joining the semiconductor region at a second position deeper than a first position of the pn junction.
According to another embodiment of the present invention, there is provided a semiconductor device, further comprising: a plurality of impurity diffusion regions, and an innermost impurity diffusion region, of the plurality of impurity diffusion regions, connecting to the reverse region and the first electrode.
According to another embodiment of the present invention, there is provided a semiconductor device, further comprising: at least a first electrode electrically contacting the reverse region, at least a second electrode electrically contacting the semiconductor region, and a second reverse region surrounding the reverse region and being reversed to the second conductive type by platinum doping at a higher concentration near the first surface of the semiconductor region than the interior.
According to another embodiment of the present invention, there is provided a semiconductor device, wherein: the first electrode additionally electrically contacting the semiconductor region.
According to another embodiment of the present invention, there is provided a semiconductor device, wherein: the first electrode additionally electrically contacting the semiconductor region.
According to another embodiment of the present invention, there is provided a semiconductor device, wherein: the first electrode additionally electrically contacting the semiconductor region.
According to another embodiment of the present invention, there is provided a semiconductor device, wherein: the semiconductor region being a silicon semiconductor.
According to another embodiment of the present invention there is provided a manufacturing method for a semiconductor device, comprising the steps of: covering at least a first portion on a first main surface of a semiconductor region with an oxide film, and the semiconductor region being a first conductive type, forming a reverse region of a second conductive type in an exposed portion selected in the first main surface of the semiconductor region by doping with platinum, and the doping with platinum forming a higher concentration of platinum proximal the first main surface than an interior portion of the semiconductor region, forming a first electrode on at least the reverse region, the first electrode being in electrical connection with at least the reverse region, and forming a second electrode on at least a second main surface of the semiconductor region, the second electrode being in electrical connection with at least the second main surface.
According to another embodiment of the present invention there is provided a manufacturing method for a semiconductor, wherein: the step of forming a reverse region by doping with platinum includes a step of heat diffusing platinum from one of the exposed portion of the first main surface and the second main surface.
According to another embodiment of the present invention there is provided a manufacturing method for a semiconductor, wherein: the step of forming the reverse region includes a step of controlling a depth of the reverse region by selecting at least one of a time and a temperature for the step of step of heat diffusing platinum.
According to another embodiment of the present invention there is provided a manufacturing method for a semiconductor, comprising the steps of: covering at least a first portion on a first main surface of a semiconductor region with a oxide film, and the semiconductor region being a first conductive type, injecting impurity ions of a second conductive type into at least a first selected section the semiconductor region using the oxide film covering the first portion as a mask, heat treating the semiconductor region receiving the impurity ions, and forming at least one impurity diffusion region of the second conductive type and covering the first main surface with the oxide film, removing the oxide film from the first surface to form an exposed portion surrounding the at least one impurity diffusion region, forming a reverse region of the second conductive type in a region surrounded by the impurity diffusion region selected in the first main surface of the semiconductor region by doping with platinum, and the doping with platinum forming a higher platinum concentration nearer the first main surface than an interior portion of the semiconductor region, forming a first electrode on at least the reverse region, the first electrode being in electrical connection with at least the reverse region, and forming a second electrode on at least a second main surface of the semiconductor region, the second electrode being in electrical connection with at least the second main surface.
According to another embodiment of the present invention there is provided a manufacturing method for a semiconductor, wherein: the step of forming a reverse region by doping with platinum includes a step of heat diffusing platinum from one of the exposed portion of the first main surface and the second main surface of the semiconductor region.
According to another embodiment of the present invention there is provided a manufacturing method for a semiconductor, wherein: the step of removing the oxide film includes a step of exposing an innermost impurity diffusion region of the impurity diffusion region, and the step of forming the first electrode includes a step of forming the first electrode in contact with the innermost impurity diffusion region.
According to another embodiment of the present invention there is provided a manufacturing method for a semiconductor, wherein: the step of forming the reverse region includes a step of controlling a depth of the reverse region by selecting at least one of a time and a temperature for the step of step of heat diffusing platinum.
To achieve the above objectives, the present invention, dopes a semiconductor region of a first conductivity type with platinum, a portion of the semiconductor region near the surface that is not covered by a oxide film is reversed to a second conductivity type, and a pn junction is formed by this reverse region of the second conductivity type and the semiconductor region of the first conductivity type. The depth of the pn junction is adjusted by controlling the temperature and time for the heat diffusion of platinum.
According to this invention, the pn junction is formed by the reverse region of the second conductivity type formed by doping with platinum and the semiconductor region of the first conductivity type. Therefore, the pn junction is shallower than that of the related art, and the position of the pn junction coincides with a position where there is effective action of platinum.
The above, and other objects, features, and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.